Microwave ovens provide a convenient means of cooking and reheating food items. Many combinations of materials of different character have been used in microwave packaging to influence the effect of the microwave energy on the food product being heated. These microwave packaging materials may be microwave transparent, for example, paper, paperboard, or many plastics, or they may be microwave energy interactive, for example, metal foils or thin metal deposits. Microwave transparent materials generally provide, for example, food product support, packaging form, insulation, and/or vapor barrier functions in packaging. Microwave energy interactive material generally provides, for example, enhanced surface heating, microwave shielding, enhanced microwave transmission, and/or energy distribution functions in packaging.
Microwave packaging often is created and configured of both microwave transparent and microwave energy interactive materials. For example, MicroRite brand trays, which are available from Graphic Packaging International, Inc., comprise aluminum foil laminated to paperboard. The aluminum foil is typically configured in predetermined shapes that define a pattern, wherein the shapes/pattern may be formed by chemically etching away (in a caustic bath) some of the foil and/or chemical deactivation of some of the foil. The configuration of the microwave energy interactive material determines the performance characteristics of the microwave energy interactive material.